[size=small]Tube buffers used to be somewhat popular around here, among other places. There was the popular Musical Fidelity X-10 v3 as well as a few models from Chinese company Yaqin, and plenty of people swore by them. But that popularity seems to have disappeared and you rarely hear about these things anymore. I've been playing with this unit for a few months, so I'm finally ready to post some thoughts. The product is labeled as YiXin Audio MDS-623 and sells for around $160 (By the way - that listing has some of the most entertaining/unfortunate translation I've ever read - definitely check it out).[/size][size=small][/size]
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[size=small]Just what exactly is a tube buffer? In a nutshell, it slots in between the analog outputs of your source (CD player, DAC, music server, whatever) and the inputs to your preamp or integrated amp. In this case it can also work with a plain old power amp since this particular unit has a volume control. So to a degree this could be called a single-source tube preamp if that's easier to handle. Most other tube buffers I've seen did not have the volume control. [/size][size=small][/size]
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[size=small]In any case, a tube buffer is exactly that - a buffer. The best explanation I can find is from Purity Audio, who markets their own (rather expensive) tube buffer called the Harmony. HERE is their info - keeping in mind that they are trying to sell you their product, this still sums it up rather well. [/size]
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[size=small]DESIGN[/size][size=small][/size]
[size=small]The MDS-623 is different than the Yaqin tube buffers (but similar to the Musical Fidelity) in that it doesn't have tubes protruding from the top. It does give you a window on the front panel to remind you they are there. Unfortunately they chose a bright LED to light up the tubes when in use, which is a choice I would not have made. It's not as bad as it sounds.... okay, maybe it is. [/size][size=small][/size]
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[size=small]The enclosure itself feels fairly sturdy if not quite as refined as some of my other gear. But it looks nice enough and doesn't call attention to itself (until you turn it on and the lights show up). The body is always black but the front panel is available in black or silver. The volume knob is the only part that the user interacts with. Around back we find a power switch, a single pair of RCA inputs and outputs, an IEC inlet, and a voltage switch (meaning the unit will work most anywhere). [/size]
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[size=small]SPECS[/size][size=small][/size]
[size=small]Tube: JAN 5670 2pcs[/size][size=small][/size]
[size=small]Input sensitivity: 150mv[/size][size=small][/size]
[size=small]Output voltage: 1.8V (RMS THD <0.03%)[/size][size=small][/size]
[size=small]Signal to noise ratio (S / N Ratio): 94DB[/size][size=small][/size]
[size=small]Frequency Response: 10Hz-50KHz (-0.5DB)[/size][size=small][/size]
[size=small]Input Impedance: 250Kohm[/size][size=small][/size]
[size=small]Output Impedance: 600ohm[/size][size=small][/size]
[size=small]Input voltage (AC Input): 110V/220V (switch exchange)[/size][size=small][/size]
[size=small]Total power consumption: 15W[/size][size=small][/size]
[size=small]Dimension: 260 * 130 * 110 (mm) (WDH)[/size][size=small][/size]
[size=small]Net Weight: 2.8KG[/size][size=small][/size]
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[size=small]As you can see, the specs are pretty good if not amazing. SNR is slightly lower than many of the better DACs out there, so you could be potentially introducing a bit of noise into the chain. But it's still high enough where it shouldn't be glaringly obvious. [/size][size=small][/size]
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[size=small]The output impedance is 600 ohm. For most devices, that should be great. But there are a few things out there which won't do as well. For example: this Jaton Operetta amp has an input impedance of 4k ohm. If driven by this tube buffer, that gives a damping factor of less than 7 which will almost certainly result in mushy low frequency response. There aren't all that many amps with low input impedance like that, but it's something to be aware of. [/size]
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[size=small]SOUND[/size][size=small][/size]
[size=small]First off, I need to explain the tube situation. The stock tubes are JAN GE 5670 which are a surprisingly solid tube to start with. I believe there is a cheaper version of the MDS-623 available that sells for $25 less, comes with cheaper tubes (Chinese 6N3 I think) and uses lesser quality parts like capacitors and such. But I don't know much about that model. Anyway, the stock JAN tubes were used for the majority of my listening. I did try some more expensive tubes - Western Electric 396A ($80/pair) and Bendix 6385 Red Bank (~$250/pair when you can find them). I realize these are unlikely matches for a $160 tube buffer device, but they are the only ones I had access to. Both of these were very slightly better than the stock JAN tubes, especially the Bendix, but honestly the improvement was not proportional to the price. There aren't that many cheaper tubes that will work in this application and be an improvement over the stock, so I'm happy with the direction they went. I'd probably buy this "upgrade" version over the base model though - the tubes alone are worth $20, and the upgraded parts are almost certainly worth the remainder of the $5 difference.[/size][size=small][/size]
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[size=small]To be honest I did not really have high hopes for this thing. How can adding an extra stage in your signal path make it sound better? But I tried to be as objective as possible because I do know of people who have used tube buffers and liked the result. I figured the best case scenario would be a pleasing coloration, a sort of "fixed EQ" if you will. [/size][size=small][/size]
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[size=small]I'll cut to the chase here - In many cases, the tube buffer did very little to the sound. In a few cases it actually degraded the sound, and in a few others it seemed to improve it. I'm actually pretty impressed - by not doing anything to the sound, that means the device is pretty transparent. [/size][size=small][/size]
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[size=small]The situations where I didn't like the result came when using high-end equipment. I didn't like the MDS between my Violectric V800 DAC and V200 amp. It seemed to round the edges, smother the soundstage, and make the whole thing a little dull. But this is to be expected since the Violectric gear is really on a higher level altogether. The same happened when using other high end combos: Anedio D2 and Analog Design Labs Svetlana, Kao Audio UD2C and Icon Audio HP8, Yulong Sabre D18 and A18. So it seems once you cross a certain performance threshold the tube buffer doesn't bring much to the table. [/size][size=small][/size]
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[size=small]Situations where I didn't hear much difference: between the Yulong D100 mkII and the Lake People G103, or between the Matrix Cube and the Matrix M-Stage, or between the Audiotrak DR DAC2 DX and the Apex Butte. Not to say there was zero difference, but the effect was so minor as to be not really worth discussing in depth. I can summarize it as a vague "softening" of the music, with perhaps a little more "ease" to the presentation. How can this be? I notice the 1.8Vrms output - slightly lower than the redbook standard 2Vrms, which possibly causes the minor differences I hear in those combinations. Some people might take the somewhat "mellow" tone as a big difference, but to me it seemed rather minor. [/size][size=small][/size]
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[size=small]So what about the combinations where adding the tube buffer actually helps? Well, I found a few. The original Yulong D100 (not the new mkII) paired with the matching Yulong A100 amp is a great combo but can get a little bright with certain headphones. Adding the tube buffer to the mix, I had an easier time listening to certain headphones. K701, Edition 8, and all Grados were more appealing with this in the mix, as were IEMs such as the Westone AC2 and LiveWires Trips. I wouldn't call this a simple rolling-off of the highs, because it seems more graceful than that. The problematic highs do lose some volume, but also seem to have a softer attack. Transients remained strong (within the limits of each headphone or IEM design) but the whole thing became somewhat more organic and smooth. [/size][size=small][/size]
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[size=small]I noticed similar improvement when using the Matrix Quattro DAC with matching Quattro amp. When used in balanced mode, this combo sounds really nice. But when I switch to single ended operation it gets a tad hot up top, and the tube buffer again comes to the rescue. For some headphones or IEMs (1964-T, Heir 8.A, Signature Pro) the regular single ended performance is fine. But for those others, the tube buffer is welcome.[/size][size=small][/size]
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[size=small]I also used the tube buffer as a simple preamp, connecting the Yulong D18 to the Emotiva Airmotiv5 active speakers. The potentiometer handling volume control of the MDS-623 is from Tokyo Cosmos aka TOCOS, and I've heard some of their pots sound pretty unbalanced in other products. My particular unit is nicely done though, with just a hint of channel imbalance at very low levels. Overall this made for an acceptable solution (the Yulong D18, unlike many of the other recent flagship DACs, has no volume control) if not a brilliant one. I love the sound made by the AMT high frequency driver in the Airmotiv5, and it doesn't really need to be "tamed". But overall it was a very listenable solution and it would probably do even better if the speakers in question were a bit on the bright side.[/size]
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[size=small] Lastly, I tried a few players that I have around the house that are not known for their audio quality. I tried a Toshiba HD-A30 HD DVD player (remember those?), a Sony BDP-S590 Blu-Ray player, and an older Pioneer Elite DV-50a universal player (which I believe is just a rebadged version of their non-Elite DV-563a with no upgrades whatsoever). In all three cases I preferred the tube buffer to be in the chain, to take the edge off some of the digital glare these players all suffer from. It doesn't magically turn them into giant-killers but it does improve things and actually helped me enjoy the Pioneer again. I haven't used it in years because it was just too rough around the edges when placed in an otherwise competent setup. So in this area the tube buffer really did prove useful.
CONCLUSION
I'm still confused about my thoughts on this device. On the one hand, it's kind of like an audio band-aid, and it could easily be replaced by an EQ, or just by using better/more neutral gear in the first place. On the other hand, I rather enjoyed it when placed in the proper system. I can say that I've spent more time with the Yulong D100/A100/Edition 8 than I have in a long time, and this tube buffer gets all the credit for that.
Would I recommend it? Yes, for certain applications I would. It isn't the ultimate solution for all your audio woes (as some users of tube buffers may have implied) but it is a useful device and sounds good in the right context. I sort of question the value of it - wouldn't it be better to use that $160 towards a better DAC or CD player? Could be. Sometimes people get attached to the device they already have though, for looks, usability, or other factors. In those cases this tube buffer could help. [/size]
